Was extremely important for someone who learned as a native to read Polish around age of three.
First part was learning a mapping grapheme to phoneme for single symbol.
Then came a second part - for a day or three picking out that symbol from raw text of newspapers, trying to pronounce its sound every time it was found.
Then as more and more symbols were learned, looking up one symbol for a while, then another for some time, then when nearing learning a whole alphabet mixing the patterns to lookup wildly.
After memorizing some 20/26 symbols, learning the connecting the sounds, and you could read simple words by then.
But again polish is extremely regular language in that sense but a very few of irregular short symbol sequences.
Yes. Subvocalisation is a fundamental part of reading. Even in scripts that (ostensibly) have no ruleset for phonemic mapping (e.g. Chinese), written language has a "voice" for accomplished readers.